Determination of Average Cone Tip Resistance

The minimum mean value of the cone tip resistance qc s determined by the minimum value of the mean of the cone tip resistance qc over the influenced zone ranging from 0.7d to 4d below the pile base (d is the pile diameter). The minimum mean value of the cone tip resistance qc2 is determined over the influence zone extending from 8d above the pile base (d is the pile diameter). The procedure for obtaining the mean value of the cone tip resistance qc1, qc2 is as follows (see figure):

1)

determine two averages of the cone stress within the zone below the pile base, one for a zone depth of 0.7d and one for 0.4d along the path "a" through "b". The smaller of the two is retained. (The zone height 0.7d applies to where the cone stress increases with depth below the pile base).

2)

determine the smallest cone stress within the zone used for the Step 1

3)

determine the average of the two values per Steps 1 and 2. Step 4 is determining the average cone stress in the zone

4)

determine the average cone stress in the zone 8d above the pile base that gives the value qc. Finally, the average of the Step 3 and Step 4 values is determined.